Modernly, coaxial cable is a very popular medium over which cable operators chose to transmit their cable TV and Internet services to residential subscribers. Most homes today are equipped with coaxial cable connections. Coaxial cable is an electrical cable consisting of an inner conductor or several un-insulated conductors tightly twisted together, often surrounded by an insulating spacer, surrounded by an outer cylindrical conducting shield, and usually surrounded by a final insulating layer. The term coaxial comes from the inner conductor and the outer shield sharing the same axis. Coaxial cable is often used as a high-frequency transmission line to carry broadband signals into a subscriber's home.
However, there is a significant bandwidth limitation to coaxial cable. Only so many channels may be supported by a given coaxial cable. For example, the typical coaxial cable only supports between 60 and 120 analog channels or 120 to 240 high definition digital channels, or a mix of the two. Since coaxial cable is used for many different services such as cable TV and Internet services, there is a demand for efficient use of the existing coaxial cable bandwidth. As a result, cable systems are now providing more and more programming through the use of a technology known as switched video or switched digital video (SDV). Switched video is a network scheme for distributing video via a cable with limited capacity such as coaxial cable. Switched video sends the digital video in a more efficient manner so that additional uses may be made of the freed-up bandwidth. FIG. 1A illustrates a diagram of how switched video saves bandwidth where channels are transmitted via a cable company's coaxial cable. In FIG. 1A, the video signal is received by the network node 104 from the video headend 101 via a distribution hub 102. Note that the amount of video channels 106 and 108 received over coaxial cables 105 and 107, respectively, is the same. However, the switched video cable 107 only needs to receive the requested channels 108, whereas the non-switched video cable 105 receives the requested channels 106 as well as many unwanted channels.
Basically, switched video involves switching from many video channels on an incoming fiber optic cable to only a few channels that are being consumed by subscribers at any given time. In current fiber-coaxial systems, a fiber optic network extending from the operator's central office carries all the available video channels (e.g., 500 channels) out to a fiber optic node or “node” which services any number of homes ranging from 1 to 2000 homes. From this point, all channels are sent via coaxial cable to each of the homes. Note that only a percentage of these homes are actively watching channels at a given time. Rarely are all channels being accessed by the homes in the service group. In a switched video system, the unwatched channels do not need to be sent over the coaxial cable to the subscribers. If a channel is not currently being transmitted on the coaxial line, the distribution hub allocates a new channel and transmits the new channel to the coaxial cable via the node. If there are multiple subscribers tuning to the same broadcast station, the node will switch the station onto only one channel of the coaxial cable and all the subscribers' cable systems will tune to that frequency. Effectively, in switched video all the subscribers tuning to the same station piggy-back onto one channel of the coaxial cable. In the extreme case where all the subscribers grouped to a particular node are tuned to the same station (e.g., during the Super bowl or an important Presidential debate), only one channel of the coaxial cable will be used for all of the subscribers. On the other hand, if a particular broadcast station is not being consumed by at least one subscriber, the node will remove the station from the channels of the coaxial cable going into the subscribers' homes. In this way, the available channels on the coaxial cable are only utilized when needed.
For a switched video system to work on today's cable systems, all digital television users in a subscription group must have devices capable of communicating with the node in a compatible manner. This enhanced switched video service requires the use of two-way direct communications with the node using reverse transmitters and proprietary signaling of the cable systems. That is, the cable systems located at the subscribers' homes must be capable of communicating with the node and vice versa.
However, most consumer electronics devices such as digital video recorders (e.g., TIVO), high-definition televisions (HDTV), and Home Theater Computers (e.g., Media Centers) available on the market today do not have two-way communication capability and cannot communicate back to the node. These consumer electronic devices may be collectively referred to as Unidirectional Cable Products (UDCPs) since they are equipped with CableCARDs that can only listen to communications, and cannot respond back to the node. UDCPs built according to applicable FCC rules are unable to access switched video services due to the prohibition on reverse transmitters within these products. Manufacturers of UDCPs would like to enable users of their products to be able to take advantage of switched video programming. However, since there is currently no nationwide standard for two-way communications for the purpose of switching video today, it is not possible to design a new retail product which can be sold in any geographical location that will support switched video. As a result, the conversion to switched video may require many years to complete.
As an interim solution, a device known as a Tuning Resolver (TR) has been developed as a way to enable access to switched video services on UDCP products. The TR is an interpreting device that sits in between the UDCP device and the node. This TR provides the necessary reverse transmitter and private signaling necessary to communicate SDV tuning requests to the node. That is, the TR “resolves” the tuning information for every tune-request from a user of a UDCP and provides detailed information to the UDCP to enable access to these services. FIG. 1B illustrates a conventional system to enable switched video services on UDCP devices using a Tuning Resolver according to the prior art. In FIG. 1B, the TR 113 has two interfaces. The first interface connects to the node 104 by plugging into the coaxial cable from the node. The TR 113 lets the signal on the coaxial cable through to the UDCP 114 so that the UDCP 114 can receive the cable RF signal 116. The other interface is a connection between the TR 113 and the UDCP 114. This connection is typically a Universal Serial Bus (USB) interface that translates simple commands from the UDCP 114 over a USB 115 (such as programming that the user of the UDCP selects) to the correct protocol that the node 104 understands. The TR 113 connects in-line with the RF signal 116 from the cable system node 104 to the UDCP 115 and utilizes a USB 115 interface for additional communications between the node 104 and the UDCP 115. These additional communications are defined by a Tuning Resolver Interface (TRIF) Specification 117 (OC-SP-TRIF-101-080130). The TRIF specification provides the technical details on the communications interface between tuners with CableCards such as UDCPs and a Tuning Resolver.
FIG. 1C illustrates a conventional system to enable switched video services on a host media server such as a Media Center personal computer (PC) via an OpenCable Unidirectional Receiver (OCUR) using a Tuning Resolver according to the prior art. An OCUR is defined in the specification OC-SP-OCUR-107-080620 and is a receiver used to tune the desired broadcast channel on the network and to stream the content to the media server. In the case of the OCUR of FIG. 1C, this OCUR has been modified to implement the TRIF specification, and hence, can request switched digital video. The term “media center” refers either to a dedicated computer appliance or to specialized PC software, both of which are adapted for playing various kinds of media (music, movies, photos etc.). A media center may also allow receiving and recording cable television broadcasts. For receiving cable television broadcasts, an OCUR is used in conjunction with the media server. The OCUR is a receiver used to tune to the desired broadcast channel on the network and to stream the content to the media server. TR 113 in FIG. 1C is the same as that illustrated in FIG. 1B. Accordingly, TR 113 has two interfaces. The first interface connects to the node 104 by plugging into the coaxial cable from the node. The TR lets the signal on the coaxial cable through to the OCUR 119 so that the OCUR 119 can receive the cable RF signal 116. The other interface is a connection between the TR 113 and the OCUR 119. This connection is typically a Universal Serial Bus (USB) interface that translates simple commands from the OCUR 119 over a USB 115 to the correct protocol that the node 104 understands. The TR 113 connects in-line with the RF signal 116 from the cable system node 104 to the OCUR 119 and utilizes a USB 115 interface for additional communications between the node 104 and OCUR 119. These additional communications are defined by the TRIF Specification 117 as illustrated in FIG. 1B. Additionally, communications between the OCUR 119 and the Host Media Server 121 may occur across a USB connection or any other data bus (i.e., Ethernet, wireless). The protocol over such data buses is Digital Receiver Interface (DRI 1.0) as defined by CableLabs like TRIF. A system such as shown in FIG. 1C requires a significant and costly modification to the OCUR to implement the TRIF specification.